Certain heterostructure materials, such as Aluminum Gallium Nitride (AlGaN) and Gallium Nitride (GaN), create an electron well (i.e., a sheet of electrons) at the interface between the two dissimilar materials resulting from the piezoelectric effect and spontaneous polarization effect there between. The resulting sheet of electrons that forms at this interface is typically referred to as a Two-Dimensional Electron Gas (“2DEG”) channel. Equally applicable is a superlattice structure having a plurality of two-dimensional hole gas (2DHG) channels. Both types of structures can be referred to as “2D×G channel(s)” devices. FETs that operate by generating and controlling the electrons in the 2D×G channel are conventionally referred to as high electron mobility transistors (“HEMTs”).
By stacking a plurality of these two-material heterostructures, and with the addition of appropriate doping in the layers to maintain the presence of the 2D×G channels when stacking a plurality of heterostructure layers, the electron sheets are able to act in parallel, allowing for greater current flow through the superlattice device. When this type of FET is “on”, the superlattice device has a lower on-resistance, relative to a single heterostructure-layer device, because the multiple 2DEG channels allow a proportionally higher current to flow between the source and drain, resulting in an overall reduction in on-resistance. This type of structure has been well suited for providing an ultra low channel resistance high frequency switch.
Although these multiple heterostructure-layer devices provide a superior ultra-low resistance high frequency switch, they are not as ideally suited for forming other devices, such as highly linear amplifiers or other devices that can be formed from a single heterostructure-layer structure. Therefore, multiple heterostructure-layer devices are typically formed on an integrated circuit (or first wafer), while the single layer devices are typically formed on a separate integrated circuit (or second wafer). The two different integrated circuits can be arranged on a printed circuit board or other circuit and coupled to one another via traces to form subassemblies, such as a transceiver or other multiple component assembly. This type of configuration can result in signal losses and power losses during the transferring of signals between one integrated circuit and the other.